Precision plastic filters with a fine mesh, such as 300 micron plastic filters, are known for filtering contaminants in a variety of applications including lubricant, fuel, coolant and air systems. Such filters include a meshed net in a cup or frame and ribs spanning the cup to provide support to the meshed net.
Conventional filters are produced using a net and a frame that are produced separately. The net is then cut and fitted on the frame, followed by insert molding to fix the net to the frame. While such structures have been used in a variety of applications, they suffer from disadvantages. One of the disadvantages that these structures suffer is that the net and frame are manufactured separately and are joined in yet another manufacturing step. Thus, several manufacturing steps are needed in the production of these filters, which increases time and complexity of manufacture and therefore increases the manufacturing cost.
While injection molding is useful in manufacturing many plastic articles, such a method has not found use in manufacturing precision plastic filters. Injection molding has been found to be impractical due to difficulties in achieving uniform distribution of plastic resin material over an entire die during molding. Prior attempts at injection molding for producing precision plastic filters have been unsuccessful at keeping a consistent pattern, frame and surrounding cup.
In order to address the problems with injection molding of precision plastic filters, variations such as vacuum molding and gas assisted pressure molding have been proposed. Vacuum molding involves the creation of a vacuum in the mold space prior to injection of the plastic. This provides a pressure difference to draw the plastic into the mold space and thereby fill the mold space. In gas assisted pressure molding, the plastic is injected into the mold at high pressure to push the plastic into the mold space and cause the plastic to fill the mold space. These molding methods suffer disadvantages, however. In particular, these molding methods require non-conventional equipment that requires additional capital expense.
Accordingly, it is desirable to provide a method and apparatus for manufacturing a precision plastic filter that obviates or mitigates at least some of the disadvantages of the prior art.